Coil casing comprising interconnecting shells



Dec. 25, 1962 c. A. PURDY ,0

con. CASING COMPRISINd INTERCONNECTING SHELLS Filed March 20, 1961 2| l6I IS I8 WWW L H9] 3 33 24 lo l4 23 INVENTOR.

BY L

AIL m ys CHESTER A. PURDY Uited States Patent 3,070,766 COIL CASINGCOMPRISING INTERCONNECTING SHELLS Chester A. Purdy, Belmont, Wis.,assignor to Ransburg Electra-Coating Corp., Indianapolis, Ind., acorporation of Indiana Filed Mar. 20, 1961, Ser. No. 96,883 13 Claims.(Cl. 336-90) This invention relates to electrical apparatus and moreparticularly to a high voltage insulating barrier.

In high voltage transformers one method heretofore commonly used toinsulate the secondary coil of the transformer is to mount it on a tubeof insulating material near the center thereof, with a primary coilcarried within said tube. The insulating tube, with the secondary coilcarried around it and the primary coil carried within it, is mounted ona leg of the transformer core and the entire assembly is immersed in abath of insulating oil. In this manner, the thickness of the insulatingtube provides an insulating barrier between the two coils, and theportions of the tube projecting outwardly from either side of thesecondary coil provide an extended surface insulation path to thegrounded core and the low voltage primary coil. The insulating oil bathfilling the space between the secondary coil and the core provides thenecessary insulation between said coil and the core. As will beapparent, to provide adequate insulating thicknesses and surfaceinsulation paths of adequate length in this type of construction, it isnecessary to employ a transformer core having a large window. Thisrequires the core legs to have excessive lengths, which thus renderssuch construction relatively expensive, and necessitates the use of alarge, cumbersome transformer housing.

It is thus the general object of this invention to pro vide aninsulating barrier for a high voltage coil which will overcome thedisadvantages described above. More specifically, it is an object ofthis invention to provide an insulating barrier for a high voltage coilwhich will have a high dielectric strength, and which will be of compactsize while still providing substantial insulating thicknesses andrelatively long surface insulation paths. It is still a further objectof this invention to provide such an insulating barrier which can beeasily manufactured from inexpensive plastic material, and which can bequickly and easily mounted around a high voltage coil.

In accordance with one form of the invention, there is provided a pairof mating shells of insulating material, each of which comprises anannular web interconnecting a plurality of rims extending axiallyoutwardly from one face of said Web. The rims have diameters whichpermit the two shells to be inserted one within the other in opposedrelationship. In this opposed relationship, the shells define anenclosed annulus for encasing a high voltage coil to insulate said coilfrom the associated electrical components with which it may be employed,as the primary coil and core of a high voltage transformer. Desirably,the walls of the shell rims abut each other in interfitting engagementto releasably retain the shells in their opposed relationship.

Other objects and features of the invention will become apparent fromthe more detailed description which follows and from'the accompanyingdrawing, in which:

FIG. 1 is a transverse cross-sectional view of an in sulating barrierembodying the invention, and showing a high voltage coil carriedtherein:

FIG. 2 is an exploded isometric view of the insulating barrier shown inFIG. 1, but with portions thereof broken away; and

FIG. 3 is an isometric view of the insulating barrier shown in FIG. 1,with portions of said barrier broken 3,070,766 Patented Dec. 25, 1962away, and showing said barrier in association with a transformer coreand coil assembly.

My invention comprises an insulating barrier for a high voltage coil andincludes a pair of mating shells 10 and 12. Conveniently, the shells10and 12 may be molded from a plastic insulating material having a highdielectric strength, for example, polyethylene, polypropylene, or thelike. in the embodiment illustrated in FIGS. 1 and 2, the shell 10includes an annular web 14 integrally connected to an inner pair ofcylindrical rims 15 and 15 projecting axially from the inner edge of theweb 14, and an outer pair of cylindrical rims 16 and 16 projectingaxially from the outer edge of the web 14. Likewise, the shell 12includes an annular web 17 interconnecting an inner pair of cylindricalrims 18 and 18 projecting axially from the inner edge of said web, andan outer pair of cylindrical rims 19 and 19 projecting axially from theouter edge of the web 17. Desirably, the pairs of rims on both shells 10and 12 have the same axial lengths, and their webs 14 and 17 havesubstantially equal radii.

As shown in FIG. 1, the rims are spaced from the common axis of the twoshells to permit said rims to be received one over the other in aninterleaved relationship, so that the shells 10 and 12 define anenclosed annulus which will encase a high voltage coil 20. It is ofcourse necessary that the coil connecting wires 21 and 23 projectoutwarly through the barrier. Accordingly, each of said coil wires mayproject through a small opening formed in one of the shell webs, asillustrated at 13; or alternatively, the rims on the shells may beprovided with notches, as illustrated at 22, which will overlap when theshells are assembled in their opposed relationship to provide a smallwire-carrying opening. Conveniently, a riser 24 may be formed on theinner face of the rim 15' for reception in a mating depression in thecoil 20 to prevent said coil from rotating within said barrier and thusdisconnecting the terminal connections of the wires 21 and 23.

When the rims on the shells 10 and 12 are interleaved their axiallyextending faces abut each other and friction'ally retain the shells ininterfitting opposed relationship. As shown in FIG. 1, the faces of therims on one or both of the shells 10 and 12 may be tapered, as at 25 and26, to enhance the frictional engagement of the rims and insureretention of the shells in interfitting engagement. More importantly,however, such a tapered rim configuration provides a greater insulatingeffectiveness for any given thickness of overlapping rims than if theindividual overlapping rims had uniform thicknesses.

Present day molding techniques preclude the use of insulating plasticmaterial to form thick walled shell webs and rims. If the shell wallsare molded to a thickness in excess of about one-quarter of an inch, airpockets may be formed in the plastic which reduce its elfectiveinsulating thickness, and because of their small dielectric strength,such air pockets form internal spark gaps within the plastic. Sparkingacross air pockets causes the plastic material surrounding them toerode, resulting in a further reduction in insulating thickness, andeventually resulting in a puncture extending completely through theplastic destroying its effectiveness as an insulating barrier.

Thus, when the shells are formed as plastic moldings, the thicknesses oftheir walls becomes a limiting factor, and it is desirable to form theshells with rims and webs having wall thicknesses in the range of fromabout one thirty-second of an inch to one-quarter of an inch. When thebarrier is to be used with a coil operating at a voltage higher thanthat which a single wall of insulation can protect against, it isnecessary to employ shells having pluralities of rims at the inner andouter circumferences of their webs. The use of shells having suchpluralities of rims also provides an insulating barrier with spark pathsof extended lengths. The embodiment of my invention illustrated in thedrawings shows a barrier employing such pluralities of rims in whicheach of the shells has a pair of rims at both the inner and outer edgesof its web, with the outer pairs of rims 16 and 16 and 19 and 19'interleaved to form an insulating thickness extending around the outerperiphery of the coil 20, and the inner pairs of rims and 15 and 1S and18 inter leaved to form an insulating thickness extending around theinner periphery of the coil. This interleaving arrangement of my shellrims also provides long surface insulation paths. As will be apparentfrom FIG. 1, any surface-tracking spark from the coil 20 has to follow asinuous path along the mating surfaces of the interleaving rims on thetwo shells.

These annular insulating thicknesses and spark path lengths defined bythe shell rims may be increased or decreased by the number of rimsformed on the shells. However, to provide the necessary insulatingthicknesses at the shell webs, it may be necessary to employ more thantwo shells. Where more than two shells are employed, they are nestedtogether with their rims disposed one over the other in overlappingrelationship in the same manner as shown in the drawings. The use ofsuch additional shells will also necessarily increase the annularinsulating thicknesses and spark path lengths defined by the shell rims.However, it is to be understood that any desired number of rims may beformed at the inner and outer edges of the shell webs and that anynumber of shells greater than two may be employed without departing fromthe scope of my invention.

In FIG. 3, my insulating barrier is shown in association with atransformer core and a primary low voltage coil 32. The configuration ofmy barrier is such that the coil 32 may be received in the axiallyextending opening defined by the inner pairs of shell rims, and the coil32 with the surrounding insulating barrier containing the secondary coil20 may thus be disposed around one leg of the core 30. The interleavingshell rims provide an insulating thickness insulating the secondary coil20 carried within the shells from the primary coil 32 and from theadjacent legs of the core 30. Conveniently, to prevent rotation of thebarrier on the core 30, each of the shell webs 14 and 17 may be providedon its outer face with a pair of parallel ribs 33 which abut the sidefaces of one of the core legs adjacent the leg upon which the barrier iscarried.

It is to be understood that it is still contemplated that the assemblyshown in FIG. 3 is to be immersed in a bath of insulating oil, and thatthe interfitting relationship of the shells 10 ad 12 will allow the oilto fill the voids between said shells and the coil carried within them.i

I claim:

1. An insulating barrier for a high voltage coil, comprising a pair ofshells formed of an insulating material and defining an enclosed annulusfor encasing a high voltage coil, each of said shells comprising anannular Web interconnecting a plurality of rims projecting axially ofsaid web, said shells being disposed in opposed relationship with theirrims overlapping each other.

2. An insulating barrier as set forth in claim 1 in which the faces ofthe rims on said shells are adapted to mate with each other.

3. An insulating barrier as set forth in claim 1 in which the faces ofthe rims on said shells are provided with mating tapers.

4'. An insulating barrier as set forth in claim 1 in whichat least oneof said shells has a plurality of said rims adjacent the outerperipheral edge of its web, and the rims on said shells adjacent theirouter peripheral edges on said shells adjacent their inner peripheraledges are interleaved.

6. An insulating barrier as set forth in claim 1 in which each of saidshells has a plurality of said rims adjacent the inner peripheral edgeof its web and a plurality of said rims adjacent the'outer peripheraledge of its web, and the rims on said shells are interleaved.

7. An insulating barrier for a high voltage coil, comprising a pair ofshells formed of a plastic insulating terial and defining an enclosedannulus for encasing a high voltage coil, each of said shells comprisingan annular web interconnecting a plurality of concentric rims projectingaxially from the inner and outer peripheral edges of said web, the rimson said pair of shells being interleaved in frictional engagement witheach other for releasably retaining said shells joined together inopposed relationship, and means on at least one of said shells lockinglyengageable with a coil carried in said barrier for retaining said coilin a fixed angular position about the axis of the barrier.

8. An insulating barrier for a high voltage coil, comprising a pair ofshells formed of a plastic insulating material and defining an enclosedannulus for encasing a high voltage coil, each of said shells comprisingan annular web interconnecting a plurality of concentric rims projectingaxially from the inner and outer peripheral edges of said web, the rimson said pair of shells being interleaved in frictional engagement witheach other for releasably retaining said shells joined together inopposed relationship, and means on the outer face of at least one ofsaid shells lockingly engageable with a transformer core for retainingsaid barrier in a fixed position thereon 9. An insulating barrier for ahigh voltage coil, com-- prising a pair of shells formed from a plasticinsulating material and defining an enclosed annulus for encasing a highvoltage coil and for reception on the leg of a core, each of said shellscomprising an annular web having one: or more concentric rims projectingaxially from its outer peripheral edge and one or more concentric rimsprojecting axially from its inner peripheral edge, the rims on said pairof shells being interleaved in frictional engagement with each other forreleasably retaining said shells joined together around said coil, atleast one of said rims being engageable with said coil and having ariser lockingly' engageable with said coil for retaining said coil fromrotation within said barrier, and a pair of parallel ribs formed on theoutwardly presented faces of said webs, whereby the rims adjacent theinner edges of the webswill support the barrier on said core leg andsaid ribs will engage an adjacent pair of core legs for retaining saidbarrier in a fixed position on said core.

10. An insulating barrier for a high voltage coil, com

prising a pair of shells formed of a plastic insulating material anddefining an enclosed annulus for encasing a high voltage coil, each ofsaid shells comprising an annular web interconnecting a plurality ofconcentric rims projecting axially from the inner and outer peripheraledges of said Web, the faces of the rims on said pair of shellsfrictionally engaging each other to releasably re-- tain said shellsjoined together in opposed relationship.

11. An insulating barrier for a high voltage coil, com

prising a plurality of shells formed of plastic insulating material anddefining an enclosed annulus for a high voltage coil, each of saidshells comprising an annular web interconnecting a plurality of rimsprojecting axially of said web, said shells being disposed in opposedrelationships with their rims overlapping each other.

l2. An insulating barrier for a high voltage coil, com

prising a pair of shells formed of an insulating material and definingan enclosed annulus for encasing a high voltage coil, each of saidshells comprising an annular web interconnecting a plurality of rimsprojecting axially of said web, said shells being disposed inopposedrelationship with their rims overlapping each other, and at least one ofsaid shells being provided with one or more openir-gs through which theconnecting wires for said coil may extend.

13. An insulating barrier for a high voltage coil, comprising a pair ofshells formed of an insulating material and defining an enclosed annulusfor encasing a high voltage coil, each of said shells comprising anannular web interconnecting a plurality of rims projecting axially ofsaid web, said shells being disposed in opposed relationship with theirrims overlapping each other, and the rims on said shells being providedWith elongated slots operatively associated with each other when saidrims are in their overlapping relationship to define one or moreopenings through which the connecting wires for said coil may extend.

References Cited in the file of this patent UNITED STATES PATENTS

